Suspension system of a vehicle

ABSTRACT

A suspension system for a vehicle includes a steering knuckle for supporting a wheel which is used for steering, an upper arm for connecting an upper portion of the steering knuckle to a frame of the vehicle, and a lower arm for connecting a lower portion of the steering knuckle to a frame of the vehicle. At least one of the arms has two link members, each of which is pivotally connected to the frame of the vehicle at one end thereof and to the steering knuckle at an opposite end thereof. The link members are disposed so as to set a kingpin offset at a positive value when a cross point between the kingpin axis and the ground is located inside of a center of a contact surface between the wheel and the ground in relation to a transverse direction of the vehicle, and to increase the kingpin offset as the wheel is turned toward an outward direction so that the wheel is located radially outwardly in relation to a turning circle.

This is a continuation of application Ser. No. 07/674,211, filed Mar.25, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a suspension system for anchoringwheels used for steering to a frame of a vehicle.

2. Description of the Prior Art

Hereinafter, a fore to aft direction of the vehicle is called alongitudinal direction, and a side to side direction of the vehicle iscalled a transverse direction. Also, a location near to a centerline ofthe vehicle is called an inside location and a location distant from acenterline of the vehicle is called an outside location.

There has been known a double pivot type suspension system for avehicle. For example, Japanese Utility Model Laid-Open Publication No.64-26507 shows such a type of suspension system. This type suspensionsystem comprises a steering knuckle for supporting a wheel, and an upperarm and a lower arm respectively connecting an upper portion and a lowerportion of the steering knuckle to a frame of a vehicle. At least one ofthe arms comprises two link members, each of which is pivotallyconnected to the frame at a respective one end thereof, and to thesteering knuckle at a respective opposite end thereof.

In this type of suspension system, a kingpin axis, which is an axisaround which a wheel used for steering is turned, extends through across point between the axis of the two link members. The kingpin axismoves in response to the movement of the cross point in a horizontalplane during steering of the vehicle. As a result, a kingpin offset,which is a transverse distance between the kingpin axis and a center ofa contact surface between the wheel and the ground, varies as thekingpin axis moves.

SUMMARY OF THE INVENTION

It is, therefore, the object of the present invention to provide adouble pivot type suspension system for a vehicle wherein the vehicle isstabilized against braking during turning by using the variation of thekingpin offset during steering of the vehicle.

In accordance with the present invention, there is provided a suspensionsystem for a vehicle which comprises a steering knuckle for supporting awheel which is used for steering, an upper arm for connecting an upperportion of the steering knuckle to a frame of the vehicle, and a lowerarm for connecting a lower portion of the steering knuckle to the frameof the vehicle. At least one of the arms includes two link members, eachof the link members being pivotally connected to the frame of thevehicle at one end thereof and to the steering knuckle at an oppositeend thereof. The link members are disposed so as to set a kingpin offsetat a positive value wherein a cross point between the kingpin axis andthe ground is located inside of the center of a contact surface betweenthe wheel and the ground in relation to a transverse direction of thevehicle, and increase the kingpin offset as the wheel is turned towardan outward direction in which the wheel is located radially outwardly inrelation to a turning circle.

In the present invention, there is provided a suspension system for avehicle which comprises a steering knuckle for supporting a wheel whichis used for steering, an upper arm for connecting an upper portion ofthe steering knuckle to a frame of the vehicle, and a lower arm forconnecting a lower portion of the steering knuckle to the frame of thevehicle. At least one of the arms includes two link members, each of thelink members being pivotally connected to the frame of the vehicle atone end thereof and to the steering knuckle at an opposite end thereof.The link members are so disposed as to set a kingpin offset at apositive value wherein a cross point between the kingpin axis and theground is located inside of the center of a contact surface between thewheel and the ground in relation to a transverse direction of thevehicle, and increase the kingpin offset as the wheel is turned towardan inward direction wherein the wheel is located radially inwardly inrelation to a turning circle as well as an outward direction wherein thewheel is located radially outwardly in relation to the turning circle.

Also in the present invention, there is provided a suspension system fora vehicle which comprises a steering knuckle for supporting a wheelwhich is used for steering, an upper arm for connecting an upper portionof the steering knuckle to a frame of the vehicle, and a lower arm forconnecting a lower portion of the steering knuckle to the frame of thevehicle. At least one of the arms including two link members and each ofthe link members is pivotally connected to the frame of the vehicle atone end thereof and to the steering knuckle at an opposite end thereof.The link members are so disposed as to set a kingpin offset at apositive value, wherein a cross point between the kingpin axis and theground is located inside of the center of a contact surface between thewheel and the ground in relation to a transverse direction of thevehicle, and minimize the kingpin offset when the wheel is turned at apredetermined angle toward an inward direction, wherein the wheel islocated radially inwardly in relation to a turning circle.

According to the features of the present invention, the two link membersare so disposed as to set a kingpin offset at a positive value wherein across point between the kingpin axis and the ground is located inside ofthe center of a contact surface between the wheel and the ground inrelation to a transverse direction of the vehicle, and increase thekingpin offset as the wheel is turned toward an outward direction,wherein the wheel is located radially outwardly in relation to a turningcircle from the neutral position of the wheel. Thus, when the vehicle isbraked during the turning of the same, a momentum due to a drag forceworking at the center of the contact surface between the wheel and theground, which rotates the wheel being turned toward the outwarddirection opposite to the turning direction around the kingpin axis,increases as the wheel is turned to the turning direction, so thatexcessive turning of the vehicle is restricted, and the safety of thevehicle is enhanced.

The safety of the vehicle is much more enhanced if the two link membersare so disposed as to set a kingpin offset at a positive value, whereina cross point between the kingpin axis and the ground is located insideof the center of a contact surface between the wheel and the ground inrelation to a transverse direction of the vehicle, and minimize thekingpin offset when the wheel is turned at a predetermined angle towardan inward direction, wherein the wheel is located radially inwardly inrelation to a turning circle. In this case, as the kingpin offset isminimized when the wheel is turned toward an inward direction from aneutral position, the kingpin offset increases rapidly when the wheel isturned toward the outward direction from the neutral position, so thatexcessive turning of the vehicle is remarkably restricted, and thesafety of the vehicle is still more enhanced.

The above and other objects and features of the present invention willbecome apparent from the following description of the preferredembodiments when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a suspension system in accordance with a firstembodiment of the present invention.

FIG. 2 is a front view of a suspension system in accordance with thefirst embodiment of the present invention.

FIG. 3 is a schematic perspective view showing a general arrangement ofthe suspension system of the first embodiment of the present invention.

FIG. 4 is a schematic plan view of the arrangement of FIG. 3.

FIG. 5 is a diagram showing variations in a kingpin offset.

FIG. 6 is a schematic plan view of a general arrangement of a suspensionsystem of a second embodiment of the present invention.

FIG. 7 is a schematic plan view of a general arrangement of a suspensionsystem of a third embodiment of the present invention.

FIG. 8 is a schematic plan view of a general arrangement of a suspensionsystem of a fourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 3, there is shown a suspension system accordingto a first embodiment of the present invention. The suspension system isfor anchoring a right front wheel W, which is used for steering and alsofor driving, of a FF (front-engine-front-drive) vehicle, to the frame ofthe vehicle.

In FIGS. 1 to 3, a steering knuckle 1 supporting the wheel W isconnected to and supported by the frame of the vehicle (not shown) at anupper portion thereof through an upper arm 2, while being connected toand supported by the frame of the vehicle (not shown) at a lower portionthereof through a lower arm 3. The lower arm 3 has an A shapedconfiguration. Two end points of the A shaped lower arm 3 are aligned insubstantially a longitudinal direction of the vehicle, and respectivelyconnected to and supported by the frame of the vehicle for verticalpivotal motion through rubber bushings 4, 4. The apex of the A shapedlower arm 3 is rotatably connected to the steering knuckle 1 through aball joint 5.

The upper arm 2 comprises two link members 6, 7. The link member 6 isdisposed in substantially a transverse direction of the vehicle. Thelink member 6 is connected to the frame of the vehicle through a rubberbush 8 at one end thereof and pivotally connected to the steeringknuckle 1 through a ball joint 9 at an opposite end thereof. The linkmember 7 is disposed above the link member 6 and in substantially alongitudinal direction of the vehicle. The link member 7 is connected tothe frame of the vehicle through a rubber bush 10 at one end thereof andpivotally connected to the steering knuckle 1 through a ball joint 11 atan opposite end thereof. As shown in FIG. 1, in a plan view, the linkmember 7 is disposed such that its axis, when extended, crosses an axisof the link member 6 at point P on the axis of the link member 7.Moreover, the link member 7 is located to the rear of the cross point Pin relation to the longitudinal direction of the vehicle. Though notshown in FIG. 1, the rubber bushes 8, 10 respectively comprise an innercylinder, an outer cylinder and a rubber placed into a space between thetwo cylinders. Thus, the link members 6, 7 can pivot horizontally withina limited angle determined by the resiliency of the rubber bushes 8, 10,and they can rotate around the axes of the rubber bushes 8, 10 to pivotupward and downward. In FIG. 2, there is also shown a drive shaft 12 anda shock absorber 13. The shock absorber 13 is connected to the lower arm3 at a lower end thereof and to the frame of the vehicle at an upper endthereof. A tie rod 14 of the steering system is connected to a steeringarm 15 protruding from the steering knuckle 1 through a ball joint 16.Thus, under a steering force provided through the tie rod 14, the frontwheel W, integrally with the steering knuckle 1, turns around a kingpinaxis KL.

The kingpin axis KL extends from a cross point between the lower arm 3and the steering knuckle 1, ie., the center of the ball joint 5, to thepoint P on the axis of the link member 7 where, in a plan view, the axisof the link member 6 and the axis of the link member 7 cross each other.A kingpin offset δ, which is the transverse distance between the kingpinaxis KL and the center of a contact surface between the front wheel Wand the ground, ie., a cross point between a center line CL of the frontwheel W and the ground, is set at a positive value, that is a crosspoint between the kingpin axis KL and the ground is located inside ofthe cross point between the center line CL of the front wheel W and theground in relation to the transverse direction of the vehicle. Thekingpin offset δ varies as the cross point P moves in response to theturning of the front wheel W.

The movement of the cross point P in response to the turning of thefront wheel W will be described hereinafter with reference to FIG. 4. InFIG. 4, the link members 6, 7 are indicated by solid lines when thefront wheel W is in the neutral position, by dashed lines when the frontwheel W is turned in a direction in which the wheel W is positionedradially outwardly in relation to a turning circle of the vehicle, thatis in which the front wheel W is turned so as to turn the vehicle to theleft in this embodiment. Hereinafter, this direction is called anoutward direction. The link members 6 and 7 are indicated by two-dotchain lines when the front wheel W is turned in a direction in which thewheel W is positioned radially inwardly in relation to a turning circleof the vehicle, that is in which the front wheel W is turned so as toturn the vehicle to the right in this embodiment. Hereinafter, thisdirection is called an inward direction. The link members are furtherindicated by broken lines when the front wheel W is excessively turnedto the inward direction.

As is understood from FIG. 4, the link members 6, 7 of the upper arm 2horizontally pivot around their respective connection points to theframe of the vehicle, ie., the rubber bushes 8, 10, in response to theturning of the front wheel W. Thus the cross point P between the linkmembers 6 and 7 moves along the axis of the link member 6. Morespecifically, when the front wheel W is turned to the outward directionfrom the neutral position, the cross point P moves to the outside of thevehicle along the link member 6 (P₀ to P₁ ). When the front wheel W isturned to the inward direction from the neutral position, the crosspoint P moves to the inside of the vehicle along the link member 6 (P₀to P₂ ). But this movement of the cross point P to the inside of thevehicle ceases when the cross point P overlaps the connection point ofthe link member 7 with the steering knuckle 1, ie., the ball joint 11.When the front wheel W is still further turned to the inward direction,the cross point P moves to the outside along the link member 6 (P₂ to P₃). Thus, the kingpin offset δ, as denoted by a line A in FIG. 1, iswithin a positive value wherein the cross point between the kingpin axisKL and the ground lies inside of the cross point between the centerlineCL of the front wheel W and the ground in relation to the transversedirection of the vehicle. The kingpin offset δ becomes a minimum whenthe front wheel W is turned to the inward direction to such an extentthat the cross point P overlaps the connection point of the link member7 with the steering knuckle 1, ie., the ball joint 11. When the frontwheel W is still further turned to the inward direction, or when thefront wheel W is turned to the outward direction, the kingpin offset δincreases substantially along a quadratic curve.

As described above, link members 6, 7 are so disposed as to set thekingpin offset δ at a positive value and increase the kingpin offset δwhen the front wheel W is turned to the outward direction from theneutral position. Thus, when the vehicle is braked during the turning ofthe same, a momentum, due to a drag force working on the center of thecontact surface between the front wheel W and the ground, which rotatesthe front wheel W being turned to the outward direction opposite to theturning direction around the kingpin axis KL, increases as the frontwheel W is turned to the turning direction, so that excessive turning ofthe vehicle is restricted when it is braked during the turning of thesame, and the safety of the vehicle is enhanced.

In this embodiment, as the kingpin offset δ is minimized when the frontwheel W is turned to the inward direction from the neutral position, thekingpin offset δ increases rapidly when the front wheel W is turned tothe outward direction from the neutral position, so that excessiveturning of the vehicle is remarkably restricted, and the safety of thevehicle is still more enhanced.

FIG. 6 shows a second embodiment of the present invention. In thisembodiment, the link member 6 is disposed transversely, and the linkmember 7 is disposed longitudinally. As shown in FIG. 6, in a plan view,the link member 6 is disposed such that its axis, when extended to theoutside, crosses an axis of the link member 7 at point P on the axis ofthe link member 7. Moreover, the link member 7 is located in front ofthe cross point P in relation to the longitudinal direction of thevehicle.

When the front wheel W is turned from the neutral position to theoutward direction, the cross point P moves along the axis of the linkmember 7. The link member 7 pivots to the outside of the vehicle aroundthe connection point thereof with the frame of the vehicle, ie., therubber bush 10, when the front wheel W is turned from the neutralposition to the outward direction, and pivots to the inside of thevehicle when the front wheel W is turned from the neutral position tothe inward direction. Thus, the cross point P moves to the outside ofthe vehicle when the front wheel W is turned from the neutral positionto the outward direction (P₀ to P₁ ), while it moves to the inside ofthe vehicle when the front wheel W is turned from the neutral positionto the inward direction (P₀ to P₂ ). However, if the front wheel W isturned to the inward direction so as to exceed the position where thecross point P overlaps the connection point of the link member 6 withthe steering knuckle 1, ie., the ball joint 9, the cross point P movesto the outside.

As a result, as in the first embodiment, the kingpin offset δ, asdenoted by a line A in FIG. 5, is within a positive value wherein thecross point between the kingpin axis KL and the ground lies inside ofthe cross point between the centerline CL of the front wheel W and theground in relation to the transverse direction of the vehicle. Thekingpin offset δ is minimized when the front wheel W is turned to theinward direction to such an extent that the cross point P overlaps theconnection point of the link member 6 with the steering knuckle 1, ie.,the ball joint 9. When the front wheel W is still further turned to theinward direction, or when the front wheel W is turned to the outwarddirection, the kingpin offset δ increases substantially along aquadratic curve. Thus, excessive turning of the vehicle is restrictedwhen it is braked during the turning of the same, and the safety of thevehicle is enhanced.

FIG. 7 shows a third embodiment of the present invention. In thisembodiment, the link member 6 is disposed transversely, and the linkmember 7 is disposed longitudinally and obliquely. As shown in FIG. 7,in a plan view, the link members 6 and 7 are disposed such that theiraxes, when extended to the outside of the vehicle, cross each other.Moreover, the link member 7 is located to the rear of the cross point Pin relation to the longitudinal direction of the vehicle.

Thus, the cross point P moves to the outside of the vehicle when thefront wheel W is turned form the neutral position to the outwarddirection (P₀ to P₁ ), while it moves to the inside of the vehicle whenthe front wheel W is turned from the neutral position to the inwarddirection (P ₀ to P₂ ). However, if the front wheel W is turned to theinward direction so as to exceed the position where the cross point Poverlaps the connection point of the link member 6 with the steeringknuckle 1, ie., the ball joint 9, the cross point P moves to theoutside.

As a result, as int he first embodiment, the kingpin offset δ, asdenoted by a line A in FIG. 5, is within a positive value wherein thecross point between the kingpin axis KL and the ground lies inside ofthe cross point between the centerline CL of the front wheel W and theground in relation to the transverse direction of the vehicle. Thekingpin offset δ is minimized when the front wheel W is turned to theinward direction to such an extent that the cross point P overlaps theconnection point of the link member 6 with the steering knuckle 1, ie.,the ball joint 9. When the front wheel W is turned to the outwarddirection, the kingpin offset δ increases substantially along aquadratic curve.

FIG. 8 shows a fourth embodiment of the present invention. In thisembodiment, the disposition of the link members 6 ad 7 is almost thesame as in the first embodiment. However, in this embodiment, when thefront wheel W is in the neutral position, the connection point of thelink member 7 with the steering knuckle 1, ie., the ball joint 11, islocated on the axis of the link member 6 in a plan view. In other words,the cross point P is located on the axis of the link member 7 in a planview when the front wheel W is in the neutral position.

Thus, the cross point P moves to the outside of the vehicle when thefront wheel W is turned from the neutral position to the outwarddirection (P₀ to P₁ ). Also, the cross point P moves to the outside ofthe vehicle when the front wheel W is turned from the neutral positionto the inward direction (P₀ to P₂ ).

As a result, the kingpin offset δ, as denoted by a line B in FIG. 5, iswithin a positive value wherein the cross point between the kingpin axisKL and the ground lies inside of the cross point between the centerlineCL of the front wheel W and the ground in relation to the transversedirection of the vehicle. The kingpin offset δ is minimized when thefront wheel W is in the neutral position. When the front wheel W isturned to the inward direction or outward direction from the neutralposition, the kingpin offset δ increases substantially along a quadraticcurve.

In the aforementioned embodiments, the upper arm 2 comprises the twolink members 6 and 7. The present invention is also effective when thelower arm 3 comprises two link members. In this case, the longitudinallydisposed link member should be on the side of the cross point which isopposite to the side thereof in the aforementioned embodiments.

We claim:
 1. A suspension system for a vehicle, having a front and arear, comprising:a steering knuckle for supporting a wheel which is usedfor steering; two link members for connecting an upper portion of thesteering knuckle to a frame of the vehicle, one of said two link membersextending along a first axis, the other of said two link membersextending along a second axis, the other of said two link members beingdisposed such that said second axis crosses said first axis at a firstcross point; and a lower arm for connecting a lower portion of thesteering knuckle to a frame of the vehicle, said lower arm having atleast one inner end connected to the frame of the vehicle and an outerend connected to said steering knuckle, each of said link members alsobeing pivotally connected to the frame of the vehicle at one end thereofand to the steering knuckle at an opposite end thereof, a kingpin axisbeing defined by a line extending between said first cross point and theouter end of said lower arm, said link members being so disposed as toset a kingpin offset, defined by a distance from a second cross pointbetween the kingpin axis and the ground and a center of a contactsurface between the wheel and the ground, at a positive value when saidsecond cross point is located inside of said center of said contactsurface in relation to a transverse direction of the vehicle, andincrease the kingpin offset as the wheel is turned toward an outwarddirection wherein the wheel is located radially outwardly in relation toa turning circle, wherein the one of the two link members is disposed inthe transverse direction of the vehicle and the other of the two linkmembers is disposed in a longitudinal direction of the vehicle, the twolink members being disposed such that, in a neutral position of thewheel, a connection point between the other of the two link members andthe steering knuckle is located on the first axis of the one of the twolink members in a plan view of the link members, and the other of thetwo link members extends towards the rear of the vehicle beyond the oneof the two link members.
 2. A suspension system for a vehicle, having afront and a rear, comprising:a steering knuckle for supporting a wheelwhich is used for steering; two link members for connecting an upperportion of the steering knuckle to a frame of the vehicle, one of saidtwo link members extending along a first axis, the other of said twolink members extending along a second axis, the other of said two linkmembers being disposed such that said second axis crosses said firstaxis at a first cross point; ad a lower arm for connecting a lowerportion of the steering knuckle to a frame of the vehicle, said lowerarm having at least one inner end connected to the frame of the vehicleand an outer end connected to said steering knuckle, each of said linkmembers also being pivotally connected to the frame of the vehicle atone end thereof and to the steering knuckle at an opposite end thereof,a kingpin axis being defined by a line extending between said firstcross point and the outer end of said lower arm, said link members beingso disposed as to set a kingpin offset, defined by a distance from asecond cross point between the kingpin axis and the ground and a centerof a contact surface between the wheel and the ground, at a positivevalue when said second cross point is located inside of said center ofsaid contact surface in relation to a transverse direction of thevehicle, and increase the kingpin offset as the wheel is turned towardan inward direction wherein the wheel is located radially inwardly inrelation to a turning circle as well as an outward direction wherein thewheel is located radially outwardly in relation to the turning circle,wherein the one of the two link members is disposed in the transversedirection of the vehicle and the other of the two link members isdisposed in a longitudinal direction of the vehicle, the two linkmembers being disposed such that, in a neutral position of the wheel, aconnection point between the other of the two link members and thesteering knuckle is located on the first axis of the one of the two linkmembers in a plan view of the link members, and the other of the twolink members extends towards the rear of the vehicle beyond the one ofthe two link members.
 3. A suspension system for a vehicle, having afront and a rear, comprising:a steering knuckle for supporting a wheelwhich is sued for steering; two link members for connecting an upperportion of the steering knuckle to a frame of the vehicle, one of saidtwo link members extending along a first axis, the other of said twolink members extending along a second axis; a first joint on each ofsaid link members pivotally connecting one end of each of said linkmembers to a frame of the vehicle; a second joint on each of said linkmembers pivotally connecting an opposite end of each of said linkmembers to the steering knuckle, the one of said two link members beingdisposed such that a portion of said first axis extending beyond thesecond joint of the one of said two link members crosses said secondaxis at a first cross point; a lower arm for connecting a lower portionof the steering knuckle to a frame of the vehicle, said lower arm havingat least one inner end connected to the frame of the vehicle and anouter end connected to said steering knuckle, a kingpin axis beingdefined by a line extending between said first cross point and the outerend of said lower arm, said link members being so disposed as to set akingpin offset, defined by a distance form a second cross point betweenthe kingpin axis and the ground and a center of a contact surfacebetween the wheel and the ground, at a positive value when said secondcross point is located inside of said enter of said contact surface inrelation to a transverse direction of the vehicle, and increase thekingpin offset as the wheel is turned toward an outward direction,wherein the one of the two link members is disposed in a transversedirection of the vehicle and the other of the two link members isdisposed in a longitudinal direction of the vehicle, the two link embersare disposed such that, in a neutral position of the wheel, the secondjoint of the other of the two link members is located closer to the rearof the vehicle than the first axis of the one of the tow link members ina plan view of the link members, and a major portion of the other of thetwo link members extends towards the front of the vehicle beyond thefirst cross point in said longitudinal direction.